Vehicles such as automobiles are provided with a brake system configured to exert a braking force on the vehicle by supplying a brake hydraulic pressure to a brake apparatus for each wheel according to an amount of an operation performed on a brake pedal. If this brake apparatus is, for example, a disk brake, the brake apparatus externally supplies the hydraulic pressure into a cylinder of a caliper to press a brake pad pushed by a piston against a surface of a disk, thereby generating the braking force.
One known type of disk brake of this kind is a hydraulic disk brake equipped with an electric parking brake function of generating a braking force based on driving (a rotation) of an electric motor (i.e., actuating the disk brake as a parking brake), for example, when a driver stops or parks the vehicle, in addition to generating the braking force based on the hydraulic pressure when the vehicle is running (for example, refer to Japanese Patent Application Public Disclosure No. 2010-76479).
The disk brake equipped with the electric parking brake function according to the conventional technique is configured to move the piston toward the disk by driving the electric motor when generating the braking force as the parking brake. A control apparatus (a controller), which controls the driving of the electric motor, determines that the piston generates a pressing force that should be generated (hereinafter also referred to as a target pressing force) when a current of the electric motor reaches a preset target current value (a current threshold value), and then stops driving the electric motor.
If the driver actuates the parking brake while, for example, pressing the brake pedal, the disk brake equipped with the electric parking brake function drives the electric motor with the hydraulic pressure exerted on the piston. In this case, stopping the driving of the electric motor according to the same condition as the condition when no hydraulic pressure is exerted on the piston may result in exertion of an excessive braking force as the parking brake. Therefore, a parking brake controller discussed in Japanese Patent Application Public Disclosure No. 2010-76479 corrects the target current value according to a pressure in a master cylinder (hereinafter also referred to as an M/C pressure) when starting braking the vehicle with use of the electric motor.
However, the parking brake controller discussed in Japanese Patent Application Public Disclosure No. 2010-76479 corrects the target current value only once when starting braking the vehicle with use of the electric motor. Therefore, if the hydraulic pressure exerted on the piston decreases before the current of the electric motor reaches this target current value after this correction is made, this may lead to generation of a weaker force than a force required to keep the vehicle parked, as the braking force of the parking brake. On the other hand, if the hydraulic pressure increases, this may lead to generation of an excessive force as the braking force of the parking brake.